This invention relates to a support for curtains, particularly curtains of the adjustable sun-louver type, comprising a plurality of carts fitting slidably in a slideway and being interconnected, serially to one another or in clusters, by a string for sequentially towing them along said slideway from a gathered position, where said carts are packed together, to a spread position where said carts are set at pitch distances from one another along said slideway, said string being attached to each cart by a corresponding anchor member effective to bias said string to huddle into side-by-side bights above said carts when the latter are packed together in said gathered position.
A support having the above-noted features is known from articles currently available on the market.
This prior support design has, over more traditional supports with carts interconnected by sequential towing arrangements which comprise metal or plastics reeds connecting each cart to an adjacent one, the advantage of a smoother and quieter run of the carts as these are towed along the slideway.
They are provided with anchor members for attaching the towing string to each cart, which include in one embodiment a reed made fast with the cart at an upper portion of the latter (between the cart and the back of the tubular slideway wherealong the cart is to run) and so bent over as to define a socket wherein the towing string can be clamped to make it fast with its corresponding cart.
The string socket is curvilinear and bent over such that the entry and exit sections of the string form a smaller angle than 180.degree. therebetween, and are therefore convergent toward the socket on the cart. This arrangement encourges the towing string to set into side-by-side bights, in a substantially sinusoidal pattern, as the carts are towed toward the gathered position.
It has been common practice to use a relatively strong and stiff string flattened in cross-section and laid on edge (with the major axis vertical) so as to be stiffer in the vertical direction. The string is subjected to a heat-setting treatment to further enhance its stiffness. This is done in order to prevent string bights from sagging down between adjacent carts to block them by nesting in between the carts and the slideway.
A first drawback of supports of that type is that the longest pitch distance between carts is restricted to the maximum string length that can be huddled in the manner just described within the slideway (which length is approximately twice the cross dimension of the slideway). This maximum pitch distance is to be obtained, where the anchor member for the string locates at one transverse end of the cart, i.e. close against one longitudinal wall of the slideway, such that the string bights can reach as far as the opposite slideway wall. In fact, the string tends to arrange itself into orthogonal bights with the longitudinal walls of the slideway, and if they are to be crowded together and stretched smoothly, it is necessary that they be not squeezed against the opposite wall of the slideway. This arrangement, however, brings about a further problem inasmuch as, with the point of attachment of the string to the cart offset from the vertical axis of the latter, the pull applied to the string in order to displace the carts will generate a moment tending to cock the carts in the slideway. To resist this natural tendency to a cocked position during operation, the carts have to be designed with a suitably longer dimension along a parallel direction to the slideway axis, which results in increased space requirements for the carts when in the gathered position.
An added problem is then brought about by the relative stiffness of the towing string, made necessary as noted above to prevent the latter from festooning or sagging down in between adjacent carts. This stiffness implies some springback in said string, with the carts in the gathered position, tending to push the carts apart. In addition, this same stiffness, when compounded with the bend imparted to the string by the anchor members, will set up an elastic reaction tending to resist full spreading of the carts along the slideway and to produce a springback pull therebetween.